This invention relates to a method for treating a semi-conductor wafer and in particular, but not exclusively, to what is known as planarisation.
It is common practice in the semi-conductor industry to lay down layers of insulating material between conducting layers in order to prevent short circuits. If a layer of insulating material is simply deposited in the normal way undulations begin to build up as the layers pass over the metallic conductors which they are designed to insulate. Various techniques have been developed to try to overcome this problem by filling the trenches or valleys between the conductors to a height above the top of the conductors so that after treatment a generally planar layer exists on the top of the wafer. One example of such a technique is to spin on layers of polyimide to smooth out the surfaces. However, in practice, narrow trenches tend to be incompletely filled whilst wide valleys are not fully levelled. As the 2-D dimensions of devices are reduced, these problems are accentuated.